/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.hbase.zookeeper.client;

/**
 * This interface specifies the public interface an event handler class must
 * implement. A ZooKeeper client will get various events from the ZooKeepr
 * server it connects to. An application using such a client handles these
 * events by registering a callback object with the client. The callback object
 * is expected to be an instance of a class that implements Watcher interface.
 * 
 */
public interface Watcher {

	/**
	 * This interface defines the possible states an Event may represent
	 */
	public interface Event {
		/**
		 * Enumeration of states the ZooKeeper may be at the event
		 */
		public enum KeeperState {
			/** Unused, this state is never generated by the server */
			@Deprecated
			Unknown(-1),

			/** The client is in the disconnected state - it is not connected
			 * to any server in the ensemble. */
			Disconnected(0),

			/** Unused, this state is never generated by the server */
			@Deprecated
			NoSyncConnected(1),

			/** The client is in the connected state - it is connected
			 * to a server in the ensemble (one of the servers specified
			 * in the host connection parameter during ZooKeeper client
			 * creation). */
			SyncConnected(3),

			/**
			 * Auth failed state
			 */
			AuthFailed(4),

			/**
			 * The client is connected to a read-only server, that is the
			 * server which is not currently connected to the majority.
			 * The only operations allowed after receiving this state is
			 * read operations.
			 * This state is generated for read-only clients only since
			 * read/write clients aren't allowed to connect to r/o servers.
			 */
			ConnectedReadOnly(5),

			/**
			  * SaslAuthenticated: used to notify clients that they are SASL-authenticated,
			  * so that they can perform Zookeeper actions with their SASL-authorized permissions.
			  */
			SaslAuthenticated(6),

			/** The serving cluster has expired this session. The ZooKeeper
			 * client connection (the session) is no longer valid. You must
			 * create a new client connection (instantiate a new ZooKeeper
			 * instance) if you with to access the ensemble. */
			Expired(-112);

			private final int intValue; // Integer representation of value
										// for sending over wire

			KeeperState(int intValue) {
				this.intValue = intValue;
			}

			public int getIntValue() {
				return intValue;
			}

			public static KeeperState fromInt(int intValue) {
				switch (intValue) {
				case -1:
					return KeeperState.Unknown;
				case 0:
					return KeeperState.Disconnected;
				case 1:
					return KeeperState.NoSyncConnected;
				case 3:
					return KeeperState.SyncConnected;
				case 4:
					return KeeperState.AuthFailed;
				case 5:
					return KeeperState.ConnectedReadOnly;
				case 6:
					return KeeperState.SaslAuthenticated;
				case -112:
					return KeeperState.Expired;

				default:
					throw new RuntimeException("Invalid integer value for conversion to KeeperState");
				}
			}
		}

		/**
		 * Enumeration of types of events that may occur on the ZooKeeper
		 */
		public enum EventType {
			None(-1), NodeCreated(1), NodeDeleted(2), NodeDataChanged(3), NodeChildrenChanged(4);

			private final int intValue; // Integer representation of value
										// for sending over wire

			EventType(int intValue) {
				this.intValue = intValue;
			}

			public int getIntValue() {
				return intValue;
			}

			public static EventType fromInt(int intValue) {
				switch (intValue) {
				case -1:
					return EventType.None;
				case 1:
					return EventType.NodeCreated;
				case 2:
					return EventType.NodeDeleted;
				case 3:
					return EventType.NodeDataChanged;
				case 4:
					return EventType.NodeChildrenChanged;

				default:
					throw new RuntimeException("Invalid integer value for conversion to EventType");
				}
			}
		}
	}

	abstract public void process(WatchedEvent event);
}
